Today I want to reveal some more science that aids the artisan glass worker. It is the result of spotting the recommended use of Aloe Vera gel as a substitute for a more expensive commercial liquid stringer medium product by glass fusers.

On the one hand, glass fusers make a lot of noise about keeping glass scrupulously clean to minimise the risk of devitrification and then do the exact opposite by using a variety of materials such as PVA glues (such as the oft-recommended Elmer’s Glue) and now, it seems, Aloe Vera gel.

On the other hand, I don’t like to see fellow glass fusers use a cheap and inferior substitute for a commercial product when there is an even cheaper product that is even more versatile and of greater purity than the substitute.

Do you want to continue wasting your money on expensive products for the rest of your life or will you learn a little science and save yourself some money instead? Good. Keep reading…

About Carboxymethylcellulose
Today I am going to talk about carboxymethycellulose. Yes, it’s a mouthful but with practise you can become a scientist and impress your friends by saying it with ease. Just break it up into car-boxy-me-thile-cell-you-low-s or just say CMC instead.

CMC is a widely used manufactured substance that is used to thicken or stiffen a liquid that otherwise might be too runny. It is also used to suspend (or carry) other materials within its matrix. CMC is found as an ingredient in many foods, such as tortillas, or in the products of sugar crafting.

From this description of CMC you will perhaps realise that CMC is a substance that can be used as a thickener or to make a solid jelly-like material, just like gelatine or agar. Gums are not the same thing even though some of their uses are similar.

In addition to food use, CMC turns out to be rather useful for glass fusers and for exactly the same reasons it is used in the food industry. It does the job that Aloe Vera gel would do, but without the expense or anti-bacterial properties. More to the point, you can control whether the CMC is used in its sol phase or its gel phase and rest assured that it definitely burns away cleanly in your kiln.

CMC is a powder that you mix with water. When CMC and water are mixed together it will either result in a sol phase or a gel phase. When CMC is in its gel phase it is firm or ‘set’, just like the jelly-like solid you find in a cold pork pie or in an aspic dish (see http://en.wikipedia.org/wiki/Aspic). When CMC is in its sol phase it is like a liquid, anywhere from being a runny mixture through to a thick viscous mixture, just like what you would see in the same pork pie or aspic when it is warm. So, you see that even cookery can be seen as a form of chemistry!

Something else you should notice, particularly in the case of aspic, is that viscous substances and jelly-like substances can be used to suspend other foods within them.

It is the relative amounts of CMC and water that affect how CMC will behave. A tiny amount of CMC in a large volume of water does not make much difference and you get a runny mixture. But when you add more and more CMC the water gets thicker and thicker (more viscous) and can flow (we’re in the sol phase) until a point is reached where it will no longer flow and has become a solid jelly-like substance that has set (we’re in the gel phase).

Glass fusers can take advantage of both the sol and gel phases of CMC.

If you make up a mixture of CMC and water that results in the sol phase it can act as a viscous carrier for materials like powdered frit that can be squirted out of a bottle. This is the basis of several liquid stringer formulations.

If you make up a mixture of CMC and water that results in the gel phase it can act as a firm carrier for materials like powdered frit that stays immobile. This is the basis of Flexi-Glass Medium.

This fascinating behaviour is explained by what CMC. In the sol phase you can imagine CMC as being lots of individual threads that are floating around in the water. As the mixture gets more concentrated those threads increase in number get increasingly tangled and eventually reaches a point where there are so many tangles that the threads can hold solid particles in place. Another way of thinking about the tangles of threads are that they are also holding liquid water inside their matrix. It’s the ‘cellulose’ part of the CMC name that tell me all of this and, in part, tells me that it will burn away cleanly!

But enough of science. It’s time to introduce someone worthy of praise…

So, dear reader, I’m not the clever inventive person. He is. And you’ll find other people sharing their recipe elsewhere on the Internet if you look hard enough.

Commercial Product based on CMC
As an inquisitive person I like to know what I’m paying for so I routinely ask for, or search out, Manufacturer Safety Data Sheets (MSDS). They contain a lot of useful information and can quite often reveal why one product seems to be better than another. Comparing similar products can reveal common themes, not just in terms of health and safety issues.

I’ve already mentioned Mr La Londe’s development of Liquid Glass Line Medium, in which the key ingredient is CMC. But what did I discover? What other products use CMC?

A commercial product called Liquid Stringer Medium is produced by Fusion Headquarters Inc. It is fundamentally based on the same idea as Liquid Glass Line Medium in that it uses CMC as the carrier medium. However, their formulation also contains other things. The addition of volatile liquids, such as glycol ether and ethyl alcohol probably do nothing more than accelerate the drying process. The MSDS for Liquid Stringer Medium can be found here at the Alpine Stained Glass web site.

Another commercial product from Fusion Headquarters Inc, also based on CMC, is Flexi-Glass Medium. It also contains glycol ether and ethyl alcohol, like their Liquid Stringer Medium, so will have the same purpose. The Flexi-Glass Medium also contains components like PVA. PVA glue is exactly what many glass fusers use as a glue and even a small child can tell you that PVA becomes a solid when it left to set. The MSDS for Flexi-Glass Medium can be found here at the D&L Art Glass Supply web site.

Another commercial product making use of CMC is called Glass Clay and is manufactured by Charmed By Alaska. Unsurprisingly, the other key component is glass powder. The MSDS for Glass Clay can be found here at the D&L Art Glass Supply web site. Something I found rather interesting in the MSDS for Glass Clay is that it is described as patent pending 2009. I find this interesting because Mr La Londe says he developed the technique of using glass frit with CMC in 1993. Maybe the basis of their patent application is the use of organic honey powder – I’ve not bothered to find out.

Finally, I should mention a variation on the theme – Bullseye’s Glastac fusing glue. Glastac does not make use of CMC. Instead it uses a related substance called hydroxypropylmethylcellulose. It’s the cellulose word that tells you it’s those long threads that get tangled up. It’s why glastac isn’t so runny as water. You’ll find the MSDS here at the D&L Art Glass Supply web site.

So, maybe I have you hooked and you want to know how to buy CMC and how to use it.

Buying Your Own CMC
Remember that CMC is actually a chemical called carboxymethycellulose and that there are also trade names for the exact same chemical, such as Tylo. Something to be careful about is whether you are buying an industrial (or technical) grade CMC or whether it is classed as a food-grade chemical.

If you like melting glass and enjoy cooking it would make sense to purchase a food-grade CMC like Tylo. Something to bear in mind is that a small quantity of CMC goes a long way – for every cup of water you need just one or two hundredths of a cup of CMC.

Tylo/CMC has a shelf life of one or two years, but if all you’re doing is burning it off in your kiln there’s no need to worry if it has gone past its Best Before date. Also, there are several grades of Tylo/CMC being sold. You do not need to waste money on ultrafine grades.

You will find Tylo/CMC available at a good retailer as well as online at places like eBay.

DIY formulation
Mr La Londe gives us a clear recipe of how he makes-up his Liquid Glass Line Medium and has been very kind to provide it in the free extract of his book (and update it). The only problem I found is that the recipe is given in terms of tablespoons and pints. Other people give their recipe in terms of cups. I work on a smaller scale and with the mindset of a scientist so deal in grams and millilitres, and very conveniently, a millilitre of water happens to weigh one gram.

So, at a smaller scale, I will describe what I do and my experiences with CMC. I hope that my comments add to what Mr La Londe has already given to us.

Before You Start:

What you are aiming for is approximately 50% frit, 48.5% water and 1.5% CMC by weight.

You will have to experiment, because different brands of CMC will behave differently.

Only if you have hard water should you consider using distilled or deionised water.

Making the CMC-Water Mixture:

To make 50g (about 50ml) of CMC-Water mixture, mix about 1.5g of CMC into 48.5g (48.5ml) of water in a container.

You do not need to mix CMC with hot water. You can use cold water.

Use a spoon or wooden stick to stir it, and/or leave it awhile (maybe even overnight) to remove the lumps.

You are aiming for a sol-phase mixture that is still liquid, but rather stiff. It should slowly creep when you tip the container.

This mixture will freeze successfully, if you make too much.

To the 50g of CMC-Water mixture, add approximately 50g of powder frits. I find the exact amount varies. A good mixture seems to have a smooth glossy sheen rather than a dull gritty texture.

You will not get it right first time. Adjust the mixture by adding more frit or more CMC-Water mixture.

Filling Your Bottles:

Use a small squeezable bottle with a thin spout, or try a bottle to which a metal tip can be attached – like you might already do with Glassline paints.

I find that 20ml soft plastic bottle work well.

Patience is needed to fill the bottle. Squeeze the bottle to expel air, cover the opening with a blob of mixture and slowly release the pressure on the bottle so that it slowly sucks-in the mixture through the narrow bottle neck.. Stiff drier mixtures will not easily suck in but those that do not have too much frit will slowly get sucked in.

The mixture should settle downwards and displace air pockets over the course of a few hours if the mixture is about right. If the mixture is too stiff then this will not happen.

Extra Hints:

Use a wooden stick to mix in extra frit, gel or water if you need to. If fresh, use gel to maintain the solidity rather than water. If old, use water to replace evaporation.

Over time the glass particles settle out because you are using the CMC in sol phase not gel phase. Keep the frits in suspension by rotating the container from time to time.

Thin plastic tips have a habit of getting blocked by a sharp particle of frit snagging, or because the mixture dries out. Use a length of wire to poke it out. Poking these problematic particles back into the bottle does nothing more than cause them to re-enter the tip and block it again.

In the picture you will see a small container of Tylo/CMC, a small plastic bowl containing CMC-Water mixture, some powder frit, a wooden stick used for mixing, a poking wire , two plastic bottles containing the finished product, an unfused example and a fused example in evidence that DIY liquid stringer really does work.

Do It Yourself
So, you now realise that CMC is the basis of Mr La Londe’s Liquid Glass Line Medium invention, Liquid Stringer Medium and Glass Clay. You also have the information you need to make your own.

The big question is whether you have the time or inclination to do your own ‘product development’ to avoid having to pay for relatively expensive products, particularly when Mr La Londe’s let the cat out of the bag and I’m giving your some extra pointers.

Here are the key points your need to remember when experimenting:

More water (or less CMC) will produce a sol phase which can flow but cannot suspend glass particles very well.

Less water (or more CMC) will produce a gel phase which will not flow and will suspect glass particles much better.

Suspended materials (such as glass frit) will settle over time, the rate depending on the ‘strength’ of your CMC mixture.

Volatile products like alcohols can substitute for some of the water to help your mixture dry-off more quickly.

Setting agents such as PVA can be used to cause the gel to solidify permanently.

Your Challenge
I leave you with three experiments to try:

Will the addition of some CMC to my watery safety flux turn it into something resembling commercial gel safety flux?

Can the instability of defrosted heaps of glass frits from the freeze-fuse technique be made more stable by using a weak CMC mixture instead of water?

Will a tiny amount of washing-up liquid or glycerine if help with ease of flow or surface tension?

Sorry for the delay in replying Kat and thank you for your question. My little tub of CMC does not contain dextrin. It is pure CMC. I would be inclined to avoid formulations that contain “other stuff” like dextrin so I suggest you look again but use different search words. In addition to “CMC” and “carboxy methyl cellulose” and “carboxymethyl cellulose” you could also try “Tylo” and “Tylose”. Adding the search term “pure” might help restrict the list to things like “99%” pure which is close enough. Only buy a small quantity as it will last a long time – unless you also want to take up sugar crafting.